What You Need to Know About Body Mass Index

Written by Michael Hunter, MD, and originally published on 27 September, 2021 in BeingWell.

THERE IS NO “PERFECT WEIGHT” that applies to all of us. Body Mass Index (BMI) measures how healthy your weight is, based on your height. BMI has become a standard health assessment tool in my radiation oncology office and many healthcare facilities. But is BMI outdated?

We begin with a definition of BMI. Body mass index measures body fat based on height and weight that applies to adult men and women. If you want to calculate your BMI, there are many online resources. For example, the US National Heart, Lung, and Blood Institute offers this remarkably easy-to-use one:

What You Need to Know About Body Mass Index | Data Literacy | Data Literacy  

Belgian mathematician Lambert Adolphe Jacques Quetelet developed the Body Mass Index in 1832. He aimed to estimate the degree of overweight and obesity in populations quickly. This determination would help government optimize health resources and financial allocations.

Better yet, use an online BMI calculator, such as the one provided above. Once you have your BMI, you can compare it to the BMI scale:

What You Need to Know About Body Mass Index | Data Literacy | Data Literacy  

Image by nagualdesign, shared under CC BY-SA 4.0, via Wikimedia Commons

While there is no perfect weight or body mass index that is universal, BMI provides some insight into your risk of health-related problems. But does the BMI represent an oversimplification of what being healthy represents?

In recognition of different statures worldwide, some countries have modified what defines normal. For example, Asian men and women have a higher risk of heart disease at a lower body mass index than non-Asians.

Using the World Health Organization (WHO) Asian BMI risk cut points, the three categories are 18.5–22.9 kg/m2 (normal weight), 23–27.5 kg/m2 (overweight), and ≥27.5 kg/m2 (obese).

Is there value in knowing one’s BMI? A 2017 study showed that those with a body mass index of 30 or greater (obese) had a 1.5 to 2.7-times higher risk of death over a 30-year follow-up. A separate 2014 study demonstrated a 1.2-fold increase in early death from all causes and heart disease compared with those with a normal body mass index.

BMI is flawed

In summary, BMI (while flawed in many ways) provides a general estimate of health risk. Body mass index should not be the only measure of your health.

Thank you for joining me today.

What You Need to Know About Body Mass Index | Data Literacy | Data Literacy  

Dr. Michael Hunter has degrees from Harvard, Yale, and Penn.

He is a radiation oncologist in the Seattle area.

You can find him regularly posting at www.newcancerinfo.com.